The present disclosure relates generally to a compact, polarization-insensitive antenna operative for transmitting or receiving electromagnetic waves in mutually orthogonal polarization planes at the same time, and to a method of making such an antenna and, more particularly, to using such an antenna with a radio frequency (RF) identification (RFID) reader, especially one configured for handheld, mobile use, for scanning RFID tags oriented at different orientations and associated with items contained in a controlled area, advantageously for inventory control of the RFID-tagged items.
RFID systems are well known and are commonly utilized for item tracking, item identification, and inventory control in manufacturing, warehouse, and retail environments. Briefly, an RFID system includes two primary components: a reader (also known as an interrogator), and a tag (also known as a transponder). The tag is a miniature device associated with an item to be monitored and is capable of responding, via a tag antenna, to an electromagnetic wave wirelessly propagated by a reader antenna of the reader. The tag responsively generates and wirelessly propagates a return electromagnetic wave back to the reader. The return electromagnetic wave is modulated in a manner that conveys identification data (also known as a payload) from the tag back to the reader. The identification data can then be stored, processed, displayed, or transmitted by the reader as needed. The return electromagnetic wave can also be used to determine the true bearing and location of the tag in a controlled area.
Due to the relatively large size and complexity of the necessary RFID components, stationary RFID readers were fixedly mounted at doorways, loading docks, and assembly lines and were the first to be developed and deployed in the field. As RFID technology matured, a need for mobile handheld RFID readers became increasingly important. Handheld RFID readers traditionally leveraged the RF antenna designs from fixed readers. However, the antenna designs for fixed readers were relatively large, heavy, costly and obtrusive, and were largely impractical for handheld reader use where compact, light, and inexpensive considerations are more important for widespread adoption.
The art has proposed various antenna designs, such as dipole antennas, for handheld RFID reader use. A dipole antenna propagates an electromagnetic wave entirely in one plane of polarization, e.g., either in a horizontal plane (horizontal polarization), or in a vertical plane (vertical polarization). The orientation of the tags in the controlled area is typically unknown, and conventional tag antennas are typically polarized in only one direction or plane: vertical or horizontal. The reader antenna and the tag antenna should be matched in polarization to obtain the best reading performance. Therefore, a horizontally polarized reader antenna is unable to accurately and quickly read a vertically polarized tag without some user manipulation or rotation of the reader and/or the tag. Likewise, a vertically polarized reader antenna is unable to accurately and quickly read a horizontally polarized tag without some user manipulation or rotation of the reader and/or the tag. However, such physical efforts slow and degrade RFID reading performance.
In practice, handheld RFID readers have traditionally needed to make significant design compromises among such factors as antenna size, antenna type, antenna performance, polarization diversity, ergonomics, and the like. For example, a circularly polarized patch antenna could be used to obtain polarization insensitivity, but at a cost in antenna gain of at least about 3 dB as compared to a linearly polarized dipole antenna. Dual dipole antennas could be used, one for each polarization, but this increases size, weight and cost. A single slanted dipole antenna could be used, but again, this increases size. Antenna gain and antenna size are proportional; hence, to obtain a desirable higher antenna gain, the antenna size must be larger, which, as noted above, is undesirable for handheld operation.
Accordingly, there remains a need for a compact, polarization insensitive, less heavy, and less costly antenna that is suitable for a handheld RFID reader for scanning RFID tags oriented at various orientations and associated with items located in a controlled area, especially for inventory control of the RFID-tagged items, as well as to a method of making and using such an antenna.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The method and structural components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.